C1.7.2a The restless Earth

Learning outcomes:Must• be able to list what happens at plate

boundariesShould• be able to describe the evidence in

favour of continental driftCould• be able to explain why Wegener's ideas

on continental drift were not generally accepted in his time

21 April 2023

What does this image suggest?Scientists thought that mountain ranges and other features were caused by the crust shrinking as the early molten Earth cooled.

Shrinking Earth theory

Alfred Wegener was the first scientist to put forward the idea of continental drift in 1915.

Other scientists refused to believe Wegener because he couldn’t explain HOW the continents moved

QuestionWhat evidence is there that Africa and South America

were once joined to each other?

https://www.youtube.com/watch?v=_5q8hzF9VVE (10 mins = Alfred Wegener)

Tectonic plates

The lithosphere (crust and upper mantle) is cracked into a number of huge pieces called tectonic plates. These plates

are moving at a speed of a few centimetres each year.

How do tectonic plates move?1) Deep within Earth, radioactive processes produce vast amounts of energy

2) This heats up substances the mantle which expand, becoming less dense, and rise towards the surface

3) Cooler material sinks

4) Convection currents form

Starter

© Snapshot Science, 2010

What has caused this damage?

Image credit: Schwede66 (Wikipedia commons)

© Snapshot Science, 2010

On September 4th New Zealand experienced its strongest earthquake in 80 years.

Why does New Zealand experience earthquakes?Image credit: USGS

https://www.youtube.com/watch?v=6Z4as_imJfM

https://www.youtube.com/watch?v=-zNyVPsj8zc

http://www.bbc.co.uk/science/earth/surface_and_interior/mountain_formation#p0037825

= new Zealand mountain formation

Questions

1) Explain the main reasons for Wegener’s explanation of continental drift not being accepted at the time.2) Wegner had a doctorate from the University of Berlin. Why do you think that such a well qualified scientist wasn’t taken more seriously?

Earth moving HSW activity

In 1912 a weather scientist, Alfred Wegener (1880-1930), proposed that the continents were originally joined but gradually moved apart. This ‘continental drift’ hypothesis explained many observations.

1. Suggest a scientific question that Wegener asked. (1 mark)

2. QWC question: What was his hypothesis? (1 mark)3. QWC question: Suggest a prediction he made. (1 mark)4. Explain why ‘continental drift’ was a ‘theory’. (3

marks)5. How would Wegener’s theory explain the fossil in

Figure B? (2 marks)6. Suggest why moving the continents could not be

measured in 1912. (1 mark)7. Suggest a measurement unit for the speed of the

Earth’s plates. (1 mark)8. Jules Marcou, a well-respected geologist, developed

the land-bridge theory. Suggest one reason why scientists believed Marcou and not Wegener. (2 marks)

9. Arrange the observations in the article into a Venn diagram to show which observations are explained by ‘plate tectonics’ and which by ‘land bridges’. (2 marks)

10. QWC question: Write a short article about how the theory of ‘plate tectonics’ developed. (6 marks)

Peer assess

1. Suggest a scientific question that Wegener asked. (1 mark)One of: Why are the rocks in South America the same as those in Africa? Why are the fossils in South America the same as those in Africa? Why does the shape of South America seem to fit into Africa?

Peer assess

2. QWC question: What was his hypothesis? (1 mark)The position of the continents depends on the amount of time that they have been moving. OR The continents were moving.

Peer assess

3. QWC question: Suggest a prediction he made. (1 mark)Predictions include:

– It is possible to measure the speed of the continents moving.

– A continent would not stay in the same position if it was measured at two different points in time.

It would also be possible to use ‘if … then …’ phrases. For example, if we measure the position of a place on a continent at two different points in time, then we will see that the place has moved.

Peer assess

4. Explain why ‘continental drift’ was a ‘theory’. (3 marks)It allowed predictions to be made (e.g. that continents were moving), explained all the observations (e.g. the observation in Figure A), explained other observations that weren’t thought to be linked to the theory (e.g. why there were sea creatures fossils up in the mountains).

Peer assess

5. How would Wegener’s theory explain the fossils in Figure B? (2 marks)Two continents pushed into each other and the Earth rose up , lifting the fossils into their current position.

Peer assess

6. Suggest why moving the continents could not be measured in 1912. (1 mark)The resolution (sensitivity) of the instruments was not good enough.

Peer assess

7. Suggest a measurement unit for the speed of the Earth’s plates. (1 mark)mm or cm ‘per year’ or ‘per decade’ or perhaps ‘per month’.

Peer assess

8. Jules Marcou, a well-respected geologist, developed the land-bridge theory. Suggest one reason why scientists believed Marcou and not Wegener. (2 marks)Marcou was a geologist but Wegener was not.

Peer assess

9.Arrange the observations in the article into a Venn diagram to show which observations are explained by ‘plate tectonics’ and which by ‘land bridges’. (2 marks)

Peer assess10. QWC question: Write a short article about how the theory of ‘plate tectonics’

developed. (6 marks)The following points could be included:

describe the theory of ‘continental drift’ state one or more observations that supported ‘continental drift’ state one or more objections to ‘continental drift’ state one or more reasons why the objections are no longer

thought to be true state that finding the plates on the Earth’s crust altered the theory state that finding the Earth’s plates were moving altered the theory state that ‘plate tectonics’ is based on Wegener’s ‘continental drift’ the article starts with an overview paragraph the article so that the opening is followed with a series of points,

each of which has some details and some evidence to support it the article is arranged so that each point has its own paragraph the article ends with a concluding paragraph, giving a summary ‘plate tectonics’ explains how continents are moved on huge

cracked plates in the Earth’s crust ‘continental drift’ could not explain how continents could move

across the sea floor